(1) Field of the Invention
The present invention relates to a mobile communication system and, more particularly, to a mobile communication system including an Access Gateway (AGW) located between an access network accommodating a plurality of base stations and a core network.
(2) Description of Related Art
In a wireless access network, a tunnel is established between a Base Station (BS) and an Access Gateway (AGW) and user data is transmitted through the tunnel, using a mobile IP (Mobile Internet Protocol) of the IETF (Internet Engineering Task Force). The tunnel of mobile IP is established by exchanging, for example, a Registration Request (RRQ) message and a Registration Reply (RRP) message of Proxy Mobile IP (PMIP) between the BS and the AGW. The formats of RRQ message and RRP message of PMIP are disclosed in IETF RFC3344, sections 3.1 and 3.2.
Meanwhile, in a wireless access network such as UMB (Ultra Mobile Broadband)/CAN (Converged Access Network) of 3GPP2 (3rd Generation Partnership Project 2), separation between a control plane handling control messages and a user plane handling user data is pursued. For example, 3GPP2 X. S0054-100-0 v1.0, sections 4.4 and 4.6, disclose that a data path and a signaling path are separated at an AGW.
FIG. 3 shows an example of a conventional wireless access network.
A Home Agent (HA) 2 of mobile IP and an Authentication Authorization and Accounting (AAA) server 3 for performing user authentication, access authorization, and accounting are connected to a core network 1. Base Stations (BSs) 10 (10A, 10B, . . . 10N) are connected to the core network 1 via an access gateway AGW 4. Reference numeral 7 denotes a session control apparatus (SRNC: Session Reference Network Controller) and reference numerals 20 (20A, 20B, . . . ) denote mobile stations.
The AGW 4 includes an AGW unit 5 for control use which handles control messages (control packets) and an AGW unit 6 for user data forwarding which handles user data (user packets). In the following description, the AGW unit 5 for control use is referred to as a C-AGW (Control plane AGW) and the AGW unit 6 for user data forwarding as a U-AGW (User plane AGW). In the above wireless access network, control packets are forwarded via the C-AGW 5 as indicated by dotted lines, and user packets are forwarded via the U-AGW 6 as indicated by solid lines.
FIG. 4 shows a signaling sequence to be performed, for example, for establishing a tunnel for forwarding user data between a BS 10A and the AGW 4 when an AT 20A is connected to the core network 1 in the wireless access network shown in FIG. 3.
When a connection request is issued from the AT 20A, an access authentication procedure is executed between the AAA server 3 and the AT 20A via the BS 10A, SRNC 7, and C-AGW 5 (SQ10a, SQ10b, SQ10c). At this time, the BS 10A is notified from the C-AGW 5 of an IP address of C-AGW 5 as AGW-ID (SQ11) and the C-AGW 5 is notified from the AT 20A of an identifier of AT 20A (ATID) to be authenticated (SQ12).
Upon completion of access authentication of the AT 20A, the BS 10A performs configurations (SQ14a, SQ14b) to establish a wireless connection between the AT 20A and the BS 10A. After that, the BS 10A transmits to the C-AGW 5 a tunnel setup request message to establish a tunnel for forwarding user data. The tunnel setup request includes the identifier (ATID) of AT 20A. In this case, a PMIP RRQ message is transmitted as the tunnel setup request (SQ15). In the case of a system framework that allows the AGW 4 to establish a plurality of tunnels for the same AT, the BS 10A adds control information (“Primary”) for indicating the first tunnel setup to the PMIP RRQ message.
Upon receiving the PMIP RRQ message, the C-AGW 5 returns a reply message, which is a PMIP RRP message in this example, to the BS 10A (SQ16). The PMIP RRP message includes an IP address of U-AGW 6 as information (“Endpoint”) for indicating a termination point of the tunnel. Upon receiving the PMIP RRP message from the C-AGW 5, the BS 10A establishes a tunnel toward the U-AGW 6 specified by the “Endpoint” (SQ18). Thereby, the AT 20A transits into a state capable of communicating user data with a correspondent node connected to the core network 1 through the tunnel established between the BS 10A and the U-AGW 6 (SQ19a, SQ19b, SQ19c).